package summer_vacation.liulee.month8.day20150816;

/**
 * Created by Administrator on 2015/9/3.
 */
public class java45 {
    public static void main(String[] args) {
        long a=1;
        long sum=1;
        for (int i=2;i<=20;i++){
            for (int j=i;j>1;j--) {
                a = a * j * (--j);
            }
            sum=sum+a;
            a=1;
        }
        System.out.println("1!+2！+3！+4！..+20!="+sum);
    }
}
